This invention relates generally to power regulation and conversion.
Electrical power may be obtained by converting energy from a non-electrical form into electricity. As examples, electricity can be obtained from light through the use of photovoltaic cells, and from wind through the use of wind generators. Power generated through such conversion systems tends to fluctuate when the source of energy provided to the system for conversion fluctuates. Thus, as the amount of light a solar panel or array is exposed to decreases, the amount of electrical power put out by the panel or array decreases. Similarly, wind generators generate less power as the amount of wind decreases. Such systems may be referred to as time-varying power systems as their power varies over time. It should be noted that the current output of such systems could be either DC or AC, and the variances in power could be in voltage and/or current.
Unfortunately, in many systems minimum voltage, current and/or power requirements need to be satisfied for proper operation of the system. Using a battery charging system as an example, if the voltage being applied to a battery being charged drops below a threshold value, charging does not occur.
The present invention is directed to the manipulation and regulation of power provided by a time-varying power source to continuously provide power to a load by insuring that any minimum voltage or current requirements of the load are met even when the power provided by the time-varying power source itself does not satisfy the load""s minimum voltage or current requirements. For a load having a minimum voltage requirement, power from a time varying source will be boosted as necessary to insure that the minimum voltage is maintained.
It is contemplated that the methods and apparatus disclosed herein are particularly suited for use in a system in which a solar array is used to charge a battery array to insure that the voltage provided to the battery array is maintained above a minimum value even when the voltage produced by the solar array falls below the minimum value.
It is also contemplated that the methods and apparatus of U.S. application Ser. No. 09/814077, filed Mar. 19, 2002, U.S. application Ser. No. 09/499097 (currently allowed), filed Feb. 4, 2000, (U.S. Pat. No. 6,204,630), and U.S. application Ser. No. 08/518638, filed Apr. 3, 1998, each of which is herein incorporated by reference in its entirety, are particularly well suited for use, or to be adapted for use, in regulating power obtained from time-varying sources, particularly solar panels and arrays. Such a regulated power system may have a boost pre-regulator receiving power from a time-varying power source such as a solar array providing an input voltage and an input current, and having compensation networks which are dynamically adjusted for power level; and a forward converter receiving control from a current-mode controller which is in turn under the control of the boost pre-regulator, in order to achieve substantially constant duty cycle of the forward converter over the entire range of power levels. Additionally, for AC devices such as Wind Generators and Water Turbines, the pre-regulator would provide power factor correction to maintain a total harmonic distortion of the input current of 2-3% at full power, and less than 5% at all power levels. For simplicity, regulators/controllers having the characteristics described in the cited applications will be referred to as xe2x80x9cE J Controllersxe2x80x9d as all the applications have Ellen James as a common inventor. Although described in the cited applications as battery chargers, E J Controllers are applicable to loads other than batteries.
In preferred embodiments, a power system will comprise a power source providing power that varies over time; a power controller receiving varying power from the power source; and a load that receives power from the power controller; wherein power is provided constantly to the load for periods during which the power provided by the power source varies. The phrase xe2x80x9cwherein power is provided constantly to the loadxe2x80x9d is intended to indicate that the power controller manipulates the relationship between the voltage and current it provides to the load in order to meet any voltage or current requirements of the load, while staying within the limits imposed by the power provided to it. It should be readily apparent that constant provision of power to a load occurs only during operation of the system and does not occur when the system is switched off. The system will preferably provide constant power to a load, even if the impedance of the load varies, particularly if the load is a battery array and the varying impedance is caused by charging the battery array. In some such embodiments, the power output by the controller is stepped down in accordance with a charging algorithm, and in relation to the current charge of the battery array.
Some preferred systems will embody a method of charging a battery array comprising the following steps: providing a battery array to be charged; providing a solar array to be used to charge the battery array, the solar array providing power comprising a voltage; controlling the power provided to the battery array from the solar array so as to provide at least a minimum voltage to the battery array at times when the voltage provided by the solar array falls below the minimum voltage; and at all other times providing a constant power level to the battery array when the power provided by the solar array varies.
Various objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the invention, along with the accompanying drawings in which like numerals represent like components.